Presently, most television viewers receive their television signals through one of three primary media. The oldest method is through radio frequency broadcast of analog signals from earth based transmitting antennae.
In the United States, for example, each television channel is provided 6 MHz of bandwidth in the radio frequency range. The radio frequency bandwidth provided for television in the United States offers 12 channels (channels 2-13) in the very high frequency (VHF) range and an additional approximately 71 channels in the ultra high frequency (UHF) range.
Radio frequency broadcast television is an analog system. That is, the television signals are broadcast in analog form. Since transmission antennas are earth based, and transmission powers are limited by law, adequate reception is commonly limited to less than 100 miles from the transmitting antenna.
Probably the most prevalent method today is via community antenna television (CATV), more commonly called “cable television”. With cable television, television signals are received via satellite receiving antennae at a central location from signals that are transmitted from geo-stationary earth orbiting communications satellite antennae. The television signals are then transmitted from the central location over a communications network to the television sets in the homes of the various subscribers of the network.
In cable television systems, coaxial cables are run from the receiving antenna location either underground or on telephone poles to the homes of the various subscribers. Due to the analog nature of CATV signals and the attenuation of signal strength transmitted over a coaxial cable over large distances, CATV networks typically span less than a 50 mile radius. The bandwidth of cable television networks is limited by the physical characteristics of the coaxial cable. Shielded coaxial cable has an extremely wide bandwidth and can typically carry upwards of 150 channels of analog television signals (6 MHz/channel).
A more recent system which is gaining in popularity is through satellite reception directly at the home. A subscriber to such a system is provided with a small, low cost, satellite dish receiving antenna for receiving satellite transmission of digital television signals directly from a earth orbiting geo-stationary communications satellite. This type of system is commonly termed DSS (for Digital Satellite System) or DDS (for Direct Digital Satellite).
The bandwidth of DSS systems is great enough to provide over 100 channels of television.
The use of fiber optic cables to transmit television signals is now being investigated. Fiber optic television networks had been explored earlier, but most of that work, including bringing optical fiber directly into the home, had been abandoned. Particularly, fiber optic cables have extremely wide wavelength bandwidth. Attempts had been made to utilize the extremely wide bandwidth available on an optic fiber to transmit a reasonably necessary number of television stations (over 30) by wavelength division multiplexing. That is, by transmitting different channels with different wavelength light and selecting the appropriate wavelength light corresponding to the desired channel to be viewed. Such systems were generally not well received because the equipment needed to transmit/receive with many different wavelengths on a single fiber tended to be expensive and difficult to operate in a stable manner. In such prior art systems, the signal was transmitted as an analog signal.
However, with the expected increasing prevalence of digital data being transmitted to residences, fiber optic transmission means are again coming under increased scrutiny. For instance, it is envisioned that in the near future, telephone, Internet, E-mail, and television services to the home will all be digital.
While digital fiber optic communications has many significant advantages such as the ability to transmit information over extremely long distances efficiently and with little interference or loss of data, it also has some drawbacks. For instance, with current fiber optic communications technology, digital bandwidths of up to 40 Gbps (billion bits per second) are achievable. However, achieving such bandwidth is extremely expensive and, therefore, not practical for bringing television signals into individual homes. Particularly, the household node equipment for delivering television service to a home must cost on the order of a few hundred dollars in order to be practical. It is believed that a limit of about 500 Mbps to 1 Gbps of bandwidth can be practically delivered with present equipment costing no more than a few hundred dollars. A high quality digital television signal comprises about 30 to 40 Mbps, including video, audio, signaling and other components. If we assume a bandwidth of about 500 Mbps, then only about 12 to 15 channels of high quality digital television can be provided. If a single, low cost, optical fiber is to be used for telephone communications, Internet communications, and television, for instance, then the amount of that bandwidth that is available strictly for television is reduced.
Most television viewers watch just one channel or possibly two channels (with picture-in-picture technology) simultaneously. It is conceivable that viewer may also be receiving a third channel that is simultaneously being recorded by a VCR. Thus, even if three viewers in a single household each had a television tuned to view two different television programs all on different channels and each also had a VCR tuned to another different channel, there would be enough bandwidth available on a typical optical fiber to transmit the 9 different channels of television data.
In broadcast, cable and DSS television systems, all channels are transmitted simultaneously and are immediately available when a user changes a channel. With the huge selection of channels of TV programming and the instantaneous accessibility thereof, many television viewers have developed a habit of “channel surfing”. As used herein, the term “channel surfing” refers to rapidly changing channels and viewing the content being broadcast on each channel for only an extremely limited period of time, typically 2-10 seconds. For instance, during a commercial break in a program being watched by a viewer, he or she may “channel surf” to determine what programs are being shown on all or some of the other television channels.
Television viewers have become accustomed to cable television and DSS television networks that provide approximately 60 to 120 channels of simultaneous television programming that can be surfed very quickly. With current technology, digital communication over a low cost optical fiber simply does not provide sufficient bandwidth to transmit 100 or even 50 simultaneous channels of television programming.
Accordingly, it is an object of the present invention to provide a fiber optic television network that can provide the services and features which viewers have come to expect from their television services.